This invention pertains to color error diffusion, and in particular, relates to the creation, for error-diffusion use, of a unique color palette which directly relates the operating color space of a color image input device with each of the possible output colors of a color image output device which performs in, or has, another operating color space. Most especially, the present invention focuses attention of the handling of digital color image data in color spaces which do not involve luminance channels, and with respect to which a quite accurate and very pleasing “flow” of output color imaging quite accurately reflects the appearance of color imaging directly associated with the input color image device.
For the purpose of explanation and illustration herein, and not with any intention to limit what will be seen to be the broad scope of this invention, a preferred manner of practicing the invention is described especially in the context of a color image input device (input device) which is a color display device that operates in sRGB color space, and a color output device (output device) which is a printer that operates in CMYK color space. Other input color spaces very suitable for employment with respect to practice of the present invention include RGB color space and cRGB color space. Similarly, another output color space which is easily accommodated is CMY color space.
According to important characteristics of the present invention, a final created operational color palette, useable for error diffusion, is effectively created in what is referred to herein as a reverse color conversion procedure which flows from the prior creation of an appropriate calibrated color profile that is directly associated with the nature and operation of the color image input device.
According to one preferred manner of expressing the nature of the present invention, what is proposed is a color error diffusion method that is effective between a color image input device which operated in one color space and a color image output device which operates in another color space, with the steps of the method including (a) preparing a final color palette for use in a practice of vector error diffusion intermediate the color image input device and the color image output device, and (b) basing that preparation upon a reverse color conversion step which is effectively applied to a generated calibrated color profile directly associated with the operation of the color image input device. That methodology is performed in a setting wherein the color image input device's color space is one selected from the group including sRGB color space, RGB color space and cRGB color space, and the color image output device's color space is one selected from the group including CMYK color space and CMY color space.
Another way for expressing the invention is that it takes the form of a color error diffusion method which is effective between a color image input device that operates in one color space and a color image output device that operates in another color space, with, from this point of view, the steps of the method including (a) with respect to the color image input device, performing a first color conversion from that device's operating color space to a selected, transitional color space which is a generic version of the color image output device's operating color space, (b) creating an initial color palette from this first color conversion, (c) using the created initial color palette in a vector error diffusion process, preparing test color calibration images, and from these images generating a calibrated color profile which is associated with the operation of the color image input device, (d) from the generated calibrated color profile, producing a color look-up table which relates the color image input device's operating color space to the color image output device's operating color space, and (e) from the produced look-up table, and employing, effectively, the performance of a second, reverse color conversion step, preparing a final color palette which relates the color image input device's operating color space to each of the possible output colors that are producible by the color image output device in its operating color space.
The various features and advantages of the invention will now become more fully apparent as the description which follows is read in conjunction with the accompanying drawings.